Chemically root-limiting layers

Thank you for explaining about permafrost. After attending the arctic soils field course by Chien-Lu Ping, I was overly impressed at how nearly impossible it is to dig through permafrost that contains over 50% ice lenses. It is a dynamic property, but when present, it prevents root growth.

For the chemically root-restrictive horizons, the salic and sulfuric horizon do restrict root growth but only chemically. Those could be considered dynamic properties, but are certainly important enough and permanent enough to change the classification and interpretation of the soil. The natric horizon can also be physically root-restricting if the columns or prisms are more than 10cm across (very to extremely coarse). Presence of a natric horizon is important enough and permanent enough to change the classification and interpretation of the soil.

Just for consideration. I wonder why the natric horizons with very to extremely coarse prisms or columns are not at least mentioned in the same way that fragipans are listed in the definition of Root Limiting Layers in Chapter 17. They follow the same conventions in how they are used in the keys. The difference with densic, fragipan, and natric is that densic and fragipan by definition have structural cracks spaced at least 10cm apart, while the natric horizon crosses that size limit. So a natric with small structural units is not physically root-restrictive, but one with large units would behave like a sodium-rich densic horizon or fragipan. I also think some mention of the natric, salic, and sulfuric as chemically root limiting could be made in that paragraph just for explanation purpose.